Here's a question that keeps bothering me. Why is it "right" to put the SSR on the ground side of the circuit, and "wrong" to put it on the hot side? Isn't it safer to gate the hot side?

BTW, I fired up the Onyx with this SSR. It took about 20 minutes to get from room temp to 75C. The Onyx has a thick GeckoTek aluminum plate on it (great heat spreader), and borosilicate glass clamped to that plate with binder clips. The glass has a folded-over dish towel during the warm-up phase. The wire nut is a little warm. The heat sink contact area of the SSR is barely above room temperature, which concurs with what Auber says on their site (can run without a heat sink with a 12V/10A load). I think the full-bore heating load is about 11 amps. I did order a heat sink, just in case.

Seems like the PID needs to be re-done. The temperature keeps wobbling.

I'm going to put together a printable rail mount so this can be bolted to a Trick Laser MAX METAL frame.

626Pilot wrote:Here's a question that keeps bothering me. Why is it "right" to put the SSR on the ground side of the circuit, and "wrong" to put it on the hot side? Isn't it safer to gate the hot side?

It's neither right nor wrong. It should work on either side of the circuit, so long as you can keep the correct polarity on the SSR.

When telling someone else how to do something it's way easier to pick ONE solution and document that. Some people work better when given an exact solution, especially if they don't quite understand it. Doesn't mean there aren't a dozen other ways to do something.

626Pilot wrote:BTW, I fired up the Onyx with this SSR. It took about 20 minutes to get from room temp to 75C. The Onyx has a thick GeckoTek aluminum plate on it (great heat spreader), and borosilicate glass clamped to that plate with binder clips. The glass has a folded-over dish towel during the warm-up phase.

Why not throw in a 24V PSU? Tested yesterday (Duet GUI keeps nice track of time ). My bed (Onyx, 3mm Alu, boroglass) heated from 25 to 100 in just over 4 minutes...

I am DeltaCon, I have a delta, my name is Con, I am definitely PRO delta! Rostock V2 / E3D V6 / Raymond Style Heatchamber on the way!

I can get a 24VDC power supply... but then I have two printers, so I would need two of them. I already bought two 350W "LED" power supplies. Would also need two 24V Onyxes, and two 24-12V step-down converters. It would also make my standby wattage go up, but not by a terrible amount.

Pilot, you can run multiple supplies. I have an external 24V supply myself (And also for your curiousity, I switch the hot side of the 24V current). It's cheaper to do that than do all the change-over. I think I spent ~10$ on a relay to switch it between 12 and 24, and ~1$ worth of powerpoles to make the connection on the outside. I also don't use a 24V onyx, but the regular one. the 24V onyx only raises the resistance enough to reduce the extra power draw, it isn't some special version. I would also recomend adding a thermal fuse, and a cut-off relay (Make sure it's mechanical and rated for 25+ Amps DC, so that it will open). I could probably dig out the part numbers I used and document it somewhat if you'd like. Advantage is that you can drop standby power down to normal, be able to use it on the lower power draw mode, and still get the heating advantages while spending a minimal amount of money.

626Pilot wrote:So, you can use a 24V supply with a 12V onyx without anything catching fire?

Yep. The 24V onyx was originally a manufacturing/design issue. Most people seem to use the original onyx rather than a 24V one, and I haven't heard of one catching fire yet. As the page for the onyx says, can be used with 24V. resistors like the Onyx fail when exposed to too high a temperature or breakdown voltage. Obviously a commercial PCB should have a breakdown voltage above 24V. For temperature, you are controlling that, and set a threshold that should be below what it would fail at.

626Pilot wrote:Here's a question that keeps bothering me. Why is it "right" to put the SSR on the ground side of the circuit, and "wrong" to put it on the hot side? Isn't it safer to gate the hot side?

I agree, I would put an SSR in the hot side of the bed circuit.

626Pilot wrote:BTW, I fired up the Onyx with this SSR. It took about 20 minutes to get from room temp to 75C. The Onyx has a thick GeckoTek aluminum plate on it (great heat spreader), and borosilicate glass clamped to that plate with binder clips. The glass has a folded-over dish towel during the warm-up phase. The wire nut is a little warm. The heat sink contact area of the SSR is barely above room temperature, which concurs with what Auber says on their site (can run without a heat sink with a 12V/10A load). I think the full-bore heating load is about 11 amps. I did order a heat sink, just in case.

Do you have the option of turning up the power supply voltage a bit? it depends on what PSU you have, and whether it has spare power capacity. The Meanwell PSUs and the Chinese LED/CCTV PSUs have a voltage adjustment potentiometer, and the 12V versions can usually reach 14V or more, which gives 36% more heating power.

626Pilot wrote:So, you can use a 24V supply with a 12V onyx without anything catching fire?

What Xenocrates already said, plus the fact that most of "us" turn down the PSU voltage to the lowest possible setting of around 20V for must PSU's. Many here use the well known Meanwell's. I have a Delta Electronics PSU that is much easier to come by in Europe, also DigiKey carries them and sends out with free delivery worldwide.

If you throw in a 12VDC stepdown you don't even need a second PSU for the 12V circuit, and all fits into the base (of a V1/V2, not sure about a V3)

I am DeltaCon, I have a delta, my name is Con, I am definitely PRO delta! Rostock V2 / E3D V6 / Raymond Style Heatchamber on the way!

dc42 wrote:I agree, I would put an SSR in the hot side of the bed circuit.

I thought so. If the bed has +12V of potential even when the heater is supposed to be off, it's one more way for a short circuit to make something bad happen.

Do you have the option of turning up the power supply voltage a bit? it depends on what PSU you have, and whether it has spare power capacity. The Meanwell PSUs and the Chinese LED/CCTV PSUs have a voltage adjustment potentiometer, and the 12V versions can usually reach 14V or more, which gives 36% more heating power.

I'm using an ATX power supply right now, so no, but I'm going to swap that for a Meanwell 350W/12V supply pretty soon. It does have a trim pot. I definitely wouldn't mind having 36% more power, and not having to pay extra for it!

DeltaCon wrote:If you have still have any choice in it, go for more wattage. I think 350W is even less than the older Viotek atx psu SeemeCNC used to sell with the V2 (and probably V1).

On consumer level PC supplies, the wattage number is more of a marketing number than a useful number, since it's the sum of 3.3V, 5V, 12V, 5Vsb, and -12V voltage rails. You need to look at the label to see how many amps the 12V rail alone can supply and do the math if you want that expressed in watts. A typical 500W PC supply may well have LESS than 350W available for 12V. Also, PC supplies tend to exaggerate their continuous load capabilities a bit, so you need a larger fudge factor when buying them.

The industrial supplies usually can deliver pretty close to what they claim. If they didn't, their larger customers would stop buying them.

I guess I'll find out after I have everything wired up. I think the 350W supply will make some gains vs. the old Viotek (450W) because it has screw terminals, rather than skinny little 18-gauge wires. I can run 12-gauge straight to the Onyx and SSR. Also, as dc42 points out, they have trim pots that will take them higher than 12V, which an ATX power supply will not do. If that's still not good enough, I'll get a 24V supply and a step-down converter.

IMO a 350W MeanWell PSU is more than adequate for a single extrusion machine. Your bed heater takes 132W at present, so about 180W when you turn the voltage up. If the hot end heater is 40W then it will rise to 54W at the higher voltage, so we're at 234W. The stepper motors, electronics and fans will take less than 60W. So about 290W total and you still have 60W of reserve when everything is running at full power.

Just to be clear, we are talking about a 12V-only PSU here. With ATX PSUs the power is split between different rails and other considerations apply.

Turning the voltage up to 14V also increases the voltage to the fans. In theory you should connect a couple of silicon diodes in series with them to bring the voltage back down to 12V.

The V3 Onyx bed heater is about 0.9 ohms, so with a 12V power supply you see about 11A of current at full power for a total of about 140W.

Now, if you switch to 24V you will double the current to 22A and quadruple the wattage to over 500W. This is why you need a 600W 24V power supply, AND safety devices to keep the bed from overheating. With 24V heating my bed can easily achieve well over 150C if not controlled by a SSR.

In order to sleep more easily I installed two 150C thermal fuses under the Onyx bed in the well where all the wires are connected. I put them in series and glued them to the Onyx using Permatex ultra copper silicone for good thermal contact. I also added a thermal fuse in thermal contact with the heat sink of the SSR in case it overheats--but it rarely even gets warm. All thermal fuses are in series so if any one of them trips the whole string goes dead. Since the thermal fuses can't handle the 20A load of the heating current, I use current through the fuses to close a normally open relay. All the 24V power to the SSR and bed heater go through the relay.

The pin gizmo is throwing off less heat than the wire nut, and the back of the SSR is very close to room temperature. The circuit characteristics have changed enough that PID control keeps overshooting, so I have to finesse that back into shape.

I have also adopted a safety protocol that I learned the hard way, last week. I had the high-current wires on the SSR reversed, and when I turned on the PSU, the heat sink got very, very hot within a minute. This was WITHOUT the heater being turned on in the controller! I had wired it backwards, and apparently, that's what an SSR does when you do that. They are NOT bidirectional! From now on, any time I touch the SSR wiring, I will turn on the PSU (without turning on the bed heat on the controller) and keep my fingers on the heat sink for a minute. If it doesn't get hot, I probably got the wiring right.

What's a good source for an appropriately rated thermal fuse? All the ones on Amazon are either too low in amperage, or just say "Dryer" and have no published current/temperature rating.

Last edited by 626Pilot on Mon Jan 16, 2017 7:59 pm, edited 1 time in total.

Okay, this is interesting! After hand-tuning the PID variables, the heater is staying within 0.1C of set point, almost always exactly 75.0C, AND I don't have to lower the max PWM like I did before. I put that variable back up to 255 (maximum value), and it works fine. I think putting the SSR on the +12V side of the circuit is doing something to the electrical characteristics that makes it easier to hold a steady temperature than when it was gating the ground side. Maybe there is some kind of "inertia" going on.

The temperature control is very nearly as stable as it was when I wasn't using an SSR at all. In this configuration, my guess is that standard deviation is less than 0.01.

Will it work. Well, the specs say yes. A quick inspection of the pictures turns up that it's of a completely different model (A 30A 12V supply). It's not a brand I recognize (Mind you, in industrial automation, it's either a Meanwell, or one of the other name brand models.) For that matter, the brand on the supply is AC-DC, not JOYLIT. That should be a red flag to you. If you want to spend the 40$, instead of the 76$ for a meanwell, go right ahead (Seriously, 76.70.), It's your house and insurance.

No problem rhoded. I've had the good fortune to work with enough industrial equipment that I've gotten a pretty good idea of where to go looking for reasonable prices (Hint, Ebay is almost never one of them. Try Craigslist unless you're looking for Industrial robots or CNC tools, and don't mind it being used, and Mc-Master Carr is for one-offs and assortments of random parts. Go to a specialty shop for any order over 75$ or 30 pieces in a category.)